Seismograph



Patented Dec. 1, 1936 UNITED STATES PATENT OFFICE 9 Claims.

My invention relates to seismographs and more particularly to a deviceof this character embodying a coil and means associated therewith forgenerating an electrical current in the coil in response to vibrationsor movements of the instrument.

In seismographs of the character now commonly used the armature carryingthe coil is mounted on the case or support for movement therewith, and arelatively heavy magnet is yieldingly supported by the case so that uponmovement of the case the magnet will tend to remain stationary, andelectrical currents, having an amplitude directly proportional to thevibratory impulses transmitted to the instrument, will be generated inthe coil. p

. In order that instruments of this type be responsive to vibrations orsimilar movements, it is necessary to employ heavy or weighted magnetsand strong springs which impair the sensitiveness of the instrument andrequire comparatively large cases.

The principal object of my invention is, therefore, to provide aseismograph wherein the entire working mechanism constitutes theyieldingly suspended mass thus making it possible to not only decreasethe relative size of the instrument, but also to increase itssensitiveness.

A further object of the invention is to embody means in an instrument ofthis type for adjusting the width of the air gap thereby permitting awidervariation in the stillness of the suspension springs used. As aresult of the variable airgap it is also possible to adjust theinstrument more easily for use in recording seismic disturbances nearother sources of vibrations.

In accomplishing these and other objects of my invention I have providedimproved details of structure, the preferred form of which is shown intheaccompanying drawing, wherein:

Fig. 1 is aperspective view of a seismograph embodying my invention andmounted on a support shown fragmentarily. Fig. 2 is a central verticalsection of the instru- 45 ment showing particularly the mounting of thecoil, armature and magnets.

Fig. 3 is a side elevational view illustrating the armature in contactwith the supporting arm.

Fig. 4 is a diagrammatic view illustrating action of the armatureresponsive to vibrations.

Referring more in detailto the drawing:

l indicates a support which may comprise either a bar as shown, or asuitable case for hous- 55 ing a seismograph generally designated 2, and

includes a bracket 3 anchored in any convenient manner to the support asby bolts 4.

Secured to the upper and lower ends of the bracket by screws 5, or thelike, are forwardly projecting spring blades 6 and 1 respectively, foryieldingly supporting therebetween a mass 8 comprising the electricalmechanism of the seismograph and including a U-shaped bar 9, havinglateral-arms Ill.

Spacing plates H are inserted between the spring blades and thecorresponding arms of the bar to permit free flexing oi the blades, andbacking plates l2 are mounted over the outer ends of the blades;.screwsl3 being extended through aligned openings in the backing plates, bladesand spacing plates and threaded into openings M of the arms for securelyconnecting the several parts in operable relation.

A spacing bracket I5, having a lateral extens'ion I6, is secured to thelower arm in alignment with its outer end by a screw I1; and rastened tothe lateral projection by screws l8 or the like is a permanentpreferably U-shaped magnet l9 having the usual poles 20 directedupwardly and spaced from the corresponding poles of a cooperating magnet2| arranged in opposed aligned relation to the magnet IS. The magnet 2|is mounted by means such as screws 22 to the lower face of the upper arml0, and a plurality of shims 23 are inserted between the magnets andtheir mountings so that the space 24, reserved between the poles of therespective magnets, may be adjusted by removing or replacing shims tovary the width of the air gap formed by the spacing.

In order to support a coil 25 within the openings of the magnets, crossbars 26 are preferably provided having lateral flanges 21 secured inrecessed portions 28 of the magnet poles by screws 29. The cross bar ofthe lower magnet further serves to pivotally support an armature 30mounted thereon by a flexible spring blade 3| secured centrally both tothe cross bar and to the armature by welding or the like. An outer end32 of the armature projects from the instrument and is adapted tocontact a boss 33 provided on a bracket arm 34 secured by means .of afoot portion 35 and screws 36 to the support. The armature is normallyretained in contacting engagement with the bracket arm by a spring 31having its upper end anchored to a hook portion 38 of .the armature andits lower end connected to a bolt 38 adjustably secured to the ear 39 ofan anchoring plate 40, by means of adjusting nuts 4!, the anchoringplate being secured in any convenient manner to the instrument as byscrews 42 threaded into openings 63 of the lower arm iii.

Wires E 4 and 65 leading fromi the coil may be connected to any suitablemechanism for recording the movements of the seismograph on film orpaper by mechanical or electrical amplification.

Assuming a device to be constructed and assembled as described, itsoperation is as follows: The bracket 3 is attached to the support I andthe support is mounted on a body, such as the earth, in whichdisplacements or vibrations are imparted. Vibrations traveling throughthe 'earth are transmitted to the support 5 and through the bracket 3 tothe arm 34. The tenthe support due to inertia andits resilient mountingby reason of the springs 6 and 1.; Since the armature 30 is attached tothe mass through the flexible fulcrum 3|, the fulcrum point of thearmature will also tend to remain stationary in parallel relation withthe bars 26 and in the center of the space'or gap between the polepieces of the respective magnets. However, since one end of the armatureis held in contact with the boss 33 by 'means of the spring 31, thevibra- H tions imparted to the arm 34 will cause oscillatory or pivotalmovement of the armature on its flexible fulcrum 3!, as shown in Fig. 4.For example, assuming that'the arm 34 moves upwardly, the armature willtilt in an anticlockwise direction so that one end moves toward the polepiece on the left-hand side of the lower magnet and its opposite endtoward the pole piece on the right-hand side of the upper magnet (Fig.2). The fulcrum 3|, being flexible, is thus capable of bending to allowrocking movement of the armature above described. This movement of thearmature causes change of magnetic flux and sets up a current impulse inthe coil. During movement of the armature, as above described,

. the spring 31 flexes to hold the armature against the boss 33 andprevents actual contact of the armature with the pole pieces. When thevibration is reversed and the'arm 34 moves downwardly, the spring 31will contract to cause the armature to follow the arm and rock oroscillate 'in'the opposite direction so'that the ends thereof movetoward the. other pole pieces of the respective magnets which causesanother current impulse to be generated in the coil in an oppositedirection. It is,,therefore, obvious that the armature will pivot oroscillate about the fulcrum in exact conformity tothe vibrationsimparted to the arm 34 setting up'current fluctuations in the coil inconformity with the intensity and frequency of the vibrations. Bysuitable amplification means, galvanometers, and photographic apparatus,the fluctuations of the current may be amplified and recorded in amanner well known to those skilled in the art.

From the foregoing, it is apparent that I have provided a compactseismograph of simple construction, adapted to be enclosed in arelatively small case and which, due to employing the electricalmechanism as the mass or weight, is extremely sensitive.

What I claim and desire to secure by Letters Patent is:

1. A seismograph including a support vibratory in response to seismicwaves, a pair of magnets having pole pieces for establishing a magneticfield, a frame member mounting the magnets with like pole pieces spacedfrom each other to form an air gap therebetween, bars connecting thepoles of the magnets, a current conducting coil supported on the bars inthe magnetic field of the magnets, an armature, a spring blade pivotallysecuring the armature on one of said bars, a pair of spaced resilientblades secured to the support and to the frame member for yieldinglysuspending the mass including said frame mem-- ber, magnets and coilfrom the vibratory support whereby inertia of the mass retains the massin immobility during vibratory movement of the support, a bracket arm onthe support for engaging the armature, and a coil spring on the framemember yieldingly connected with the armature for holding the armaturein contact with in said air gap and responsive to vibratory movement ofthe support to generate a current in said coil which is a function ofsaid seismic waves.

2. In a device of the character described, a support, a pair of spacedresilient blades secured to the support, a frame member fixed to outerends 'of the blades,-a pair of magnets having pole pieces forestablishing a magnetic field, means mounting the magnets in the framemember with like pole'pieces spaced from each other to form an air gaptherebetween, bars connecting the pole pieces of each magnet, a currentconducting coil supported on the bars in the magnetic field of themagnets, an arm extending from said support, an armature, means forpivotally mounting the armature centrally on one of said bars and incontact with said arm, and yielding means connected with the armaturefor retaining the armature in contact with said arm so that the armatureis pivoted in said air gap responsive to vibratory movement of said armand inertia of said magnets to generate a current in said coil.

3. In a device of the character described, a support, a pair of magnetshaving poles for establishing a magnetic field, means mounting themagnets on the support with their poles in spaced aligning relation toform an air gap therebetween, an armature, means for pivotallysupporting the armature centrally within said air gap, ,means foradjusting the magnets on said mounting to vary thewidth of the air gap.

the bracket arm so that the armature is pivoted a current conductingcoil, means for supporting said coil in encircling relation with thearmature and in the field. of the magnets, and means on the supportengaging the armature for eflecting pivotal movement of the armature inresponse to vibratory movement of said support and inertia of saidmagnets to generate a current in said coil.

4. In a seismograph including a support vibratory in response to seismicwaves, a pair of opposed U-'-shaped magnets for establishing a Imagnetic field, a current conducting coil, cross bars connecting thepoles of each magnet for supporting the coil in the field of the magnet,a pair of leaf springsyieldingly mounting the magnets and coil forvibratory movement on the support whereby inertia of the mass includedin the magnets and coil retains the mass in immobility during vibrationof the support, an

. i at tory in response to seismic waves, a pair of op-' posed U-shapedmagnets for establishing a mag-' netic field, a current conducting coil,cross bars oi-connecting the poles of each magnet for supportingsaid'coil in the magnetic field oi the magnets, a pair of leaf springsyieldingly mounting the magnets and coil for vibratory move- 'mentrelatively to the support whereby inertia of the mass including themagnets and 0011' retains the mass in immobility during vibration or thesupport, an armature, a spring blade fixed to-the "crossbar one magnetand to the armature for pivotally supporting the armature within thecoil and magnetic field of the magnets, a bracket arm on the supporthaving one end engaging the armature for eflecting pivotal movement ofthe armature in 'response'to vibratory movement of the support togenerate a current in said coil which is a function of the seismicwaves, and a coil spring for pivotally retaining the armature inengagement with said arm.

6. A seismograph including a support vibratory in response to'seismicwaves, a pair of opposed U-shaped magnets having pole piecesestablishing a magnetic field, a carrier for mounting the magnets withlike 'pole pieces spaced from each other to form an air gaptherebetween, a bar connected to the poles of one of the magnets, anarmature, a spring blade secured to said bar and to said armature forpivotally mounting the armature on said bar intern mediate said poles ofthe magnets. a coil encircling said armature and supported by themagnets, springs for yieldingly mounting said carrier on the vibratorysupport whereby inertia of the massincluding said carrier; magnets, coiland bar retains said mass in immobility during vibratory 'movement orthe support; a bracket arm on the support engaging the outer end of thearmature to eflect pivotal movement oi the armature in response tovibratory movement oi the support for generating a current in said coilwhich is afunction of said seismic waves, and a coil spring mounted onthe carrier and connected with the outer end of the armature forretaining the arcross bar for connecting the poles oi-the magnet maturein pivotal engagement with the bracket '1. A seismograph including asupport, a frame, a magnet mounted in the frame for establishing a manetic field, a current conducting coil, 1:,

supported by the carrier in the field of said I the mass including saidmagnet and coil retains the mass in immobility during vibratory movementof the support, a bracket arni connecting the armature with thesupport'for effecting pivotal movement oi! the armature in response tovibratory movement of the support to effect change or the magnetic fieldsothat a current is generatedin'said coil whichisganiunction 0! saidseismic waves, and a coil spring mounted on the frame and having one endengaging the outer end of the armature for retaining the armature inpivotal engagement with the bracket arm.

8. A seismograph including a support vibratory in response to seismicwaves, a pair of magnets having poles for establishing a magnetic field.a carrier for the magnets to retain the magnets in spaced aligningrelation to form an air gap between the poles thereof, an armature, aspring blade centrally secured to one of the magnets and to the armaturefor pivotally supporting the armature within said air gap, a currentconducting coil encircling the armature and carried by said magnets, apair of resilient blades having respective ends fixed to the support andto said whereby inertia of the mass carried by said resilient bladesretains the mass in immobility during vibratory movement of the support.a bracket arm mounted on the'support and engaging the armature foreffecting pivotal movement of the armature simultaneously with vibratorymovement of the support to generate a current in said coil which is afunction of said seismic waves, and a coilspring mounted on the carrierand con-.- nected with the armature'to retain the armature in pivotalengagement with the bracket arm.

- 9. A seismograph including a support responsive to vibrations, a pairof magnets having pole pieces for establishing a magnetic field,-acarrier for themagnets to retain the magnets in spaced aligning relationto form an air gap between the.

poles thereof, a coil encircling the air gangland agnets, resilientmeans suspending said carrier from the support whereby inertia of themass including said magnets and carrier causes it to remain immobileduring vibratory movement of the support an armature. means pivotallymounting the armature midway betweewthe poles of the magnets, and meansoperably connecting an'end of the armature with the vibratory support,whereby vibrations in the support produce rocking movement of thearmature on its pivotal mounting.

f WILLIAM G. dam.

' carrier for mounting the carrier onthe support

